A variable-speed drive model, with an improved internal motor-drive system, the final production version of the Robling lathe was (unofficially) the Mk. 3a. The original Mk 3 had been obliged to carry its motor exposed between the stand plinths. The lathe below - a long-bed model 850 with the 17 pitches and feeds screwcutting gearbox - was made in 1963 and carried serial number 1795.